OSHA requirements are set by statute, standards and regulations. Our interpretation letters explain these requirements and how they apply to particular circumstances, but they cannot create additional employer obligations. This letter constitutes OSHA's interpretation of the requirements discussed. Note that our enforcement guidance may be affected by changes to OSHA rules. Also, from time to time we update our guidance in response to new information. To keep apprised of such developments, you can consult OSHA's website at http://www.osha.gov.

This is in response to your letter of December 24, 2002. On August 31, 2001, you asked OSHA some questions regarding repairs to the cord plug (attachment plug) of double-insulated tools under OSHA's construction electrical standards. We responded to those questions in a letter to you dated December 17, 2002. In your current letter, you ask us to reconsider our answer to one of those questions.

Previous letter
In our December 17, 2002, letter, we paraphrased one of your questions as follows:

Question (1): This question is posed with respect to hand power tools that are NOT designed for use in hazardous environments. Is it permissible to replace the plug of a double-insulated electric hand tool with after-market parts? Is it permissible to repair the (external) power cord?

In our answer, in applying 29 CFR 1926.302(a)(1), 1926.403(a), and 1926.449, we stated that it was not permissible to open the body of a double-insulated tool to make a repair, since that would vitiate the testing laboratory's approval of the tool as double-insulated. Specifically, in that portion of our answer, we stated:

Repair of double insulated tools

With respect to double insulated tools, competently made repairs to external parts of the tool, using parts that are at least equivalent to those used in the original tool, are permitted. For example, as long as the replacement plug is an approved item, has a capacity that meets or exceeds the original, and is properly installed, its use for repair is permitted.

However, repairs that require opening the body of a double insulated tool are not permitted under §1926.403(a) because opening the tool body would vitiate the approval of the tool (opening a double insulated tool may have deleterious effects on its double-insulation characteristics). For example, complete replacement of the power cord on a double insulated drill typically requires opening the body of the tool. Therefore, such a replacement would not be permitted under §1926.403(a). [Underlining added.]

In your current letter, you object to our conclusion that opening the body of a tool to make a repair would violate §1926.403(a) (see the portion of the answer underlined above). You assert that opening the tool body to make a repair does not, in fact, vitiate an Underwriter's Laboratory (UL) approval of the tool, and state that manufacturers supply replacement parts and instructions on how to make such repairs.

There are numerous nationally recognized testing laboratories; we are not in a position to survey them all to determine whether opening a tool that they have approved as double insulated would vitiate their approval. However, we agree that, if opening the tool body does not vitiate the testing laboratory's approval of the tool as double-insulated equipment, then opening the tool body would not, in itself, violate §1926.403(a). Therefore, we are modifying the underlined portion of our December 17, 2002, answer as follows:

Repairs that require opening the body of a double insulated tool are permitted under §1926.403(a) if opening the tool body is consistent with the terms of the testing laboratory's approval of the tool as double-insulated. For example, if the terms of the testing laboratory's approval permits a competent repair technician or facility to open the body of the tool to replace the power cord on a double insulated drill, such a repair would be permitted under §1926.403(a).

To avoid confusion, we are retracting our December 17, 2002, letter and reissuing our response with the above modification, as follows:

Question (1): This question is posed with respect to hand power tools that are NOT designed for use in hazardous environments. Is it permissible to replace the plug of a double-insulated electric hand tool with after-market parts? Is it permissible to repair the (external) power cord?

Electric power operated tools shall either be of the approved double-insulated type or grounded in accordance with Subpart K of this part [§§1926.400-1926.449].

As you know, double-insulated tools have two-prong attachment plugs instead of a grounding (third) prong.

In addition, in 29 Part CFR 1926 Subpart K, §1926.403(a) requires all electric equipment, including double-insulated tools, to be approved. "Approved" is defined in §1926.449 as being "acceptable," which (for purposes of this question) is defined as "accepted, or certified, or listed, or labeled, or otherwise determined to be safe by a qualified testing laboratory...." A double-insulated electric hand tool with its original two-prong attachment plug that has been listed by a nationally recognized testing laboratory (NRTL) would comply with §1926.302(a).(1)

With regard to the applicable provisions in the OSHA standards for inspecting these tools, §1926.404(b)(1)(iii)(C) states:

(C) Each cord set, attachment cap, plug and receptacle of cord sets, and any equipment connected by cord and plug, except cord sets and receptacles which are fixed and not exposed to damage, shall be visually inspected before each day's use for external defects, such as deformed or missing pins or insulation damage, and for indications of possible internal damage. Equipment found damaged or defective shall not be used until repaired. [Emphasis added.]

You indicated that when these plugs are found to be damaged or the strain-relief is torn, you recommend that repairs be made, in accordance with §1926.404(b)(1)(iii)(C). Enclosed with your letter was a commercially available polarized attachment plug, which you state is UL-rated and has an appropriate capacity for a double insulated tool with a 12- to 18-gauge cord. The plug is specifically designed for installation as a replacement plug.

To satisfy the requirements of the OSHA standards, a repair would have to restore the tool to its "approved" condition in accordance with §1926.403(a). Tools, such as the double-insulated ones you address, are approved as complete factory-produced entities. The approval is for the tool as a whole -- its design, capacity, materials and construction. This provision precludes the use of an approved tool if its characteristics are materially altered. Also, it requires that the repair not compromise the integrity of the double-insulated construction.

Repair of double insulated tools

With respect to double insulated tools, competently made repairs to external parts of the tool, using parts that are at least equivalent to those used in the original tool, are permitted. For example, as long as the replacement plug is an approved item, has a capacity that meets or exceeds the original, and is properly installed, its use for repair is permitted.

Repairs that require opening the body of a double insulated tool are permitted under §1926.403(a) if opening the tool body is consistent with the terms of the testing laboratory's approval of the tool as double-insulated. For example, if the terms of the testing laboratory's approval permits a competent repair technician or facility to open the body of the tool to replace the power cord on a double insulated drill, such a repair would be permitted under §1926.403(a).

In addition, the cord may be repaired by severing the cord above bad area and installing an appropriate replacement plug as described above. However, repair of a cord for a tool such as a typical electric drill by splicing is not permitted. Section 1926.405(g)(2)(iii) states:

Flexible cords shall be used only in continuous lengths without splice or tap. Hard service flexible cords No. 12 or larger may be repaired if spliced so that the splice retains the insulation, outer sheath properties, and usage characteristics of the cord being spliced.

This provision precludes the repair of flexible cords smaller than No.12 (the higher the number, the smaller the cord). Since hand power tools typically have flexible power cords smaller than No.12, those cords are not permitted to be spliced. Heavier cords -- those No. 12 or larger (that is, with a lower gauge number), may be repaired with a molded or vulcanized splice as long as the repair returns the cord to at least the equivalent of its original specifications.

Question (2):Does the metal strain-relief (metal cord clamp) of a replacement attachment plug on a double-insulated tool have to be grounded under §1926.404(f)(3) and (7) (or other standard)?

Answer: We address your grounding question with respect to use of a properly installed replacement plug with a metal sleeve for strain relief. The strain relief sleeve is designed to compress the end-cap rubber cover, which squeezes the outer protective sheath of the power cord. In this design, there is a thick layer of rubber between the metal sleeve and the power cord sheath.

For purposes of your question, the provision that would be most typically pertinent(2)is §1926.404(f)(7)(iv), which provides:

(iv) Equipment connected by cord and plug. Under any of the conditions described in paragraphs (f)(7)(iv)(A) through (f)(7)(iv)(C) of this section, exposed noncurrent-carrying metal parts of cord- and plug-connected equipment which may become energized shall be grounded:

(A) If in a hazardous (classified) location (see §1926.407).
(B) If operated at over 150 volts to ground, except for guarded motors and metal frames of electrically heated appliances if the appliance frames are permanently and effectively insulated from ground.
(C) If the equipment is one of the types listed in paragraphs (f)(7)(iv)(C)(1) through (f)(7)(iv)(C)(5) of this section. However, even though the equipment may be one of these types, it need not be grounded if it is exempted by paragraph (f)(7)(iv)(C)(6).

(1) Hand held motor-operated tools;
(2) Cord- and plug-connected equipment used in damp or wet locations or by employees standing on the ground or on metal floors or working inside of metal tanks or boilers;
(3) Portable and mobile X-ray and associated equipment;
(4) Tools likely to be used in wet and/or conductive locations;
(5) Portable hand lamps.
(6) Tools likely to be used in wet and/or conductive locations need not be grounded if supplied through an isolating transformer with an ungrounded secondary of not over 50 volts. Listed or labeled portable tools and appliances protected by a system of double insulation, or its equivalent, need not be grounded. If such a system is employed, the equipment shall be distinctively marked to indicate that the tool or appliance utilizes a system of double insulation. [Emphasis added.]

If the original double-insulated tool plug is replaced with the type of replacement plug described above, and the power cord is in good condition, then under §1926.404(f)(7)(iv) the metal strain relief clamp would not be required to be grounded because there is virtually no likelihood that the metal clamp may become energized.

If you need additional information, please contact us by fax at: U.S. Department of Labor, OSHA, Directorate of Construction, Office of Construction Standards and Compliance Assistance, fax # 202-693-1689. You can also contact us by mail at the above office, Room N3468, 200 Constitution Avenue, N.W., Washington, D.C. 20210, although there will be a delay in our receiving correspondence by mail.

Sincerely,

Russell B. Swanson, Director
Directorate of Construction

1. Section 1926.404(f)(7)(iv)(6) requires that double insulated tools be "distinctively marked to indicate that the tool or appliance utilizes a system of double insulation."[Back to Text]

2. There are a number of provisions that address grounding, including the grounding of portable and vehicle-mounted generators [§1926.404(f)(3)], and the grounding of supports, enclosures, and equipment [§1926.404(f)(7)]. There are additional references to non-current-carrying metal parts in §1926.404(f)(8) and (11). [Back to Text]

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